LeetCode - Reverse Linked List II

Reverse Linked List II

//
public ListNode reverseBetween(ListNode head, int m, int n) {
        if(head == null || m == n) return head;
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        ListNode walker = dummyNode, runner = dummyNode;
        int i=1;
        while(i < m){
            walker = walker.next;
            runner = runner.next;
            i++;
        }
        while(i < n + 1){
            runner = runner.next;
            i++;
        }
        ListNode next = runner.next;
        runner.next = null;
        ListNode cur = walker.next;
        walker.next = next;
        while(cur != null){
            ListNode temp = cur.next;
            cur.next = walker.next;
            walker.next = cur;
            cur = temp;
        }
        return dummyNode.next;
    }
// better solution 
public ListNode reverseBetween(ListNode head, int m, int n) {
        if(m==n || head==null)
            return head;
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode pre = dummy;
        int i=1;
        while(i<m){
            pre = pre.next;
            i++;
        }
        ListNode mNode = pre.next;
        ListNode cur = mNode.next;
        while(i<n && cur!=null){
            ListNode next = cur.next;
            cur.next = pre.next;
            pre.next = cur;
            mNode.next = next;
            cur = next;
            i++;
        }
        return dummy.next;
    }